Motor assembly for driving a pump or rotary device with a low inductance resistor for a matrix converter

ABSTRACT

A resistor assembly for a motor drive circuit for an electric motor assembly can have a generally circular shape. The resistor assembly includes a resistor with input and output connectors and a pair of conductor elements extending from the input and output connectors. The pair of conductor elements extend adjacent each other along a curved serpentine path so the resistor has a generally circular outer perimeter and a generally circular inner perimeter. The curved serpentine path of the pair of conductor elements allows current to flow through the pair of conductor elements so that magnetic fields generated by the current flow through the pair of conductor elements cancel each other, thereby providing the resistor with low inductance.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the application data sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Field

This disclosure relates broadly to an electric motor assembly fordriving a pump, and more particularly to an electric motor assemblyhaving a matrix converter with a low inductance resistor.

DESCRIPTION OF THE RELATED ART

Electric motors can be used in a wide variety of applications. One suchexample is industrial pumps, which are used to pump fluids, such aschemicals, in an industrial setting (e.g., a chemical manufacturingplant). Such pumps include an electric motor to drive the pump (e.g.,drive the rotation of the pump impeller).

SUMMARY

It is an object of this disclosure to provide an electric motor assembly(e.g., for use with industrial pumps) that allows precise speed controlof the electric motor and allows the electric motor to run at speedshigher than the input line frequency and allows increased pressure orflow of a pump coupled to the electric motor with the same sized pump.

In accordance with one aspect of the disclosure, a resistor assembly fora matrix converter used in a motor drive circuit for an electric motorassembly is provided. The resistor assembly has low inductance and agenerally circular shape.

In accordance with another aspect of the disclosure, a low inductanceresistor for a matrix converter used in a motor drive circuit for anelectric motor assembly is provided. The resistor has a pair ofconductor elements that extend from input and output connectors and arerouted adjacent each other so that the resistor defines a generallyannular shape. Current flows through the pair of adjacent conductorelements such that magnetic fields generated thereby cancel each otherout, thereby providing the resistor with low inductance.

In accordance with another aspect of the disclosure, a low inductanceresistor for a matrix converter used in a motor drive circuit for anelectric motor assembly is provided. The resistor has a pair ofconductor elements that extend from input and output connectors andextend adjacent each other along a curved serpentine path. Current flowsthrough the pair of conductor elements so that magnetic fields generatedthereby cancel each other out, thereby providing the resistor with lowinductance.

In accordance with another aspect of the disclosure, a resistor assemblyfor a motor drive circuit of an electric motor assembly for driving apump is provided. The resistor assembly comprises an input connector, anoutput connector, and a pair of conductor elements extending from theinput and output connectors. The pair of conductor elements extendadjacent each other along a curved serpentine path so the resistorassembly has a generally circular outer perimeter and a generallycircular inner perimeter. The curved serpentine path of the pair ofconductor elements allows current to flow through the pair of conductorelements so that magnetic fields generated by the current flow throughthe pair of conductor elements cancel each other, thereby providing theresistor assembly with low inductance.

In accordance with another aspect of the disclosure, an electric motorassembly for diving a pump is provided. The electric motor assemblycomprises an electric motor having an output shaft that extends along acentral axis of the electric motor, the electric motor being operable torotate the output shaft. The electric motor assembly also comprises amotor frame that houses the electric motor so that the output shaftprotrudes from an end of the motor frame. The electric motor assemblyalso comprises a first plate having a hub with a central openingconfigured to receive the output shaft therethrough, the first platecoupleable about the output shaft and having a cavity configured tohouse motor drive electronics. The electric motor assembly alsocomprises a resistor assembly within the cavity. The resistor assemblycomprises a case having a generally annular shape and defining a recess.The resistor assembly also comprises a resistor within the case andcomprising an input connector, an output connector, and a pair ofconductor elements extending from the input and output connectors. Thepair of conductor elements extend adjacent each other along a curvedserpentine path so the resistor has a generally curved outer perimeterand a generally curved inner perimeter, the resistor configured to be atleast partially disposed in the recess of the case. The curvedserpentine path of the pair of conductor elements allows current to flowthrough the pair of conductor elements so that magnetic fields generatedby the current flow through the pair of conductor elements cancel eachother, thereby providing the resistor with low inductance.

In accordance with another aspect of the disclosure, a plate assembly isprovided configured for use with an electric motor assembly for drivinga pump. The electric motor assembly can have an electric motor with anoutput shaft. The plate assembly comprises a hub with a central openingextending from an end wall of the plate assembly and configured toreceive the output shaft therethrough, the plate assembly coupleableabout the output shaft and having a cavity that houses motor driveelectronics. The plate assembly also comprises a resistor within thecavity. The resistor comprises an input connector, an output connector,and a pair of conductor elements extending from the input and outputconnectors. The pair of conductor elements extend adjacent each otheralong a curved serpentine path so the resistor has a generally curvedouter perimeter and a generally curved inner perimeter. The curvedserpentine path of the pair of conductor elements allows current to flowthrough the pair of conductor elements so that magnetic fields generatedby the current flow through the pair of conductor elements cancel eachother, thereby providing the resistor with low inductance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an exploded view of an electric motor assembly for driving apump or rotary device.

FIG. 1B is a partially assembled view of the electric motor assembly ofFIG. 1A, excluding the fan and shroud cover.

FIG. 2 is a schematic front view of a resistor case for use with theelectric motor assembly.

FIG. 3 is a schematic planar view of a clamp resistor for use with theelectric motor assembly.

FIG. 4A is schematic illustrations of the clamp resistor of FIG. 3during operation.

FIG. 4B is an enlarged schematic view of a portion of the clamp resistorof FIG. 4A during operation.

FIG. 5 is schematic planar view of a front surface of the resistor caseof FIG. 2 with the clamp resistor of FIG. 3 disposed therein and coveredby a dielectric material.

FIG. 6 is a schematic planar view of a rear surface of the resistor caseof FIG. 5.

FIG. 7 is schematic perspective view of the chamber of an end-plate ofthe electric motor assembly with the resistor case of FIG. 5 mountedtherein.

FIG. 8 is an exploded view of an end-plate assembly of the motorassembly and the drive module electronics therein.

FIG. 9 is a partial view of a motor side of the end-plate assembly ofFIG. 8.

FIG. 10 is a rear view of a power plane printed circuit board layerhoused in the end-plate assembly of FIG. 8.

FIG. 11 shows an assembled matrix converted in the end-plate assembly ofFIG. 8.

FIG. 12 is a schematic diagram of a matrix converter according to oneembodiment.

FIG. 13 is a schematic diagram of one embodiment of a clamp for a matrixconverter.

FIG. 14 is a schematic diagram of one embodiment of a portion ofcircuitry of a matrix converter.

FIG. 15A is a schematic diagram of a bidirectional switch according toone embodiment.

FIG. 15B is a schematic diagram of a bidirectional switch according toanother embodiment.

FIG. 15C is a schematic diagram of a bidirectional switch according toanother embodiment.

FIG. 16 is a schematic diagram of a matrix converter according toanother embodiment.

DETAILED DESCRIPTION

FIGS. 1A-2A show an example motor assembly 1000. The motor assembly 1000can be coupled to a pump (not shown) to drive the pump. The motorassembly 1000 includes an electric motor 100 with an output shaft orrotor 120. The motor 100 can be housed in a motor frame 200 so that theoutput shaft or rotor 120 protrudes from an end 210 of the motor frame200. As shown, a second end of the output shaft or rotor 120 protrudesfrom the other end of the motor frame 200, and may be coupled to thepump. The motor assembly 1000 can include a plate assembly P removablycoupleable over the output shaft or rotor 120 to the motor frame 200.The plate assembly P can include one or both of a mid-plate 300 and anend-plate 400. The plate assembly P includes a bearing 140 via which itcouples to the output shaft or rotor 120.

The mid-plate 300 can couple to the output shaft or rotor 120 via thebearing 140, which can be disposed in an opening 320 (e.g., bearinghousing or sleeve) of the mid-plate 300 (see, e.g., FIGS. 2B and 7). Themid-plate 300 can be disposed adjacent the end 210 of the motor frame200 and has a recess or cavity 340 that faces the motor frame 200. Themid-plate 300 can have one or more (e.g., a plurality of) heat sink fins310 extending from an outer surface (e.g., outer peripheral surface) ofthe mid-plate 300 to facilitate heat dissipation.

The end-plate 400 can coupled to the mid-plate 300 so that the mid-plate300 is interposed between the end 210 of the motor frame 200 and theend-plate 400. The output shaft or rotor 120 extends through an opening410 in the end-plate 400. The end-plate 400 can have a cavity 420,defined at least in part by an end wall 460, that receives an electronicmodule 700 therein, which is further discussed below.

A fan 500 couples to the output shaft or rotor 120 so that the end-plate400 is interposed between the fan 500 and the mid-plate 300. The fan 500is rotatably coupled to the output shaft or rotor 120 such that rotationof the output shaft or rotor 120 rotates the fan 500.

A shroud cover 600 can be removably disposed over the mid-plate 300,end-plate 400 and fan 500. The shroud cover 600 can removably attach(e.g., with one or more fasteners, such as screws or bolts) to the motorframe 200.

The motor assembly 1000 can further include a terminal box 600 attachedto the motor frame 200. The terminal box 600 has connector wires 610that can extend into channels 430 of a terminal box connector 440 (seeFIG. 8) of the end-plate 400 to electrically connect electronics in theterminal box 600 with electronic module 700 (see FIG. 8) in theend-plate 400. The mid-plate 300 and end-plate 400 can be made ofcopper, aluminum or cast iron.

FIG. 2 shows a front side 913 of a case 910 for use with the electricmotor assembly 1000. In one implementation, the case 910 can be made ofaluminum. However, the case 910 can be made of other suitable materials(e.g., other suitable metals). The case 910 can at least partially housea resistor 920 (see FIG. 3) as further discussed below. The case 910 hasa curved outer wall 910A. In one implementation, the curved outer wall910A can have a generally circular shape. The case 910 can include oneor more (e.g., a plurality of) fastener openings 911 along at least aportion of the curved outer wall 910A. The fastener opening(s) 911 canreceive a fastener (e.g., bolt, screw) therethrough.

The case 910 has a curved inner wall 916. In one implementation, thecurved inner wall 916 has a circular shape that defines a centralopening 919 (e.g., a circular opening) of the case 910. The case 910 caninclude one or more (e.g., a plurality of) fastener openings 918 alongat least a portion of the curved inner wall 916. The fastener opening(s)918 can receive a fastener (e.g., bolt, screw) therethrough.

The case 910 has a recess or cavity 912 defined at least in part by andbetween a base surface 912A, the curved outer wall 910A and the curvedinner wall 916. The case 910 includes a cutout or slot 914 defined by apair of spaced apart walls 914A (e.g., generally parallel walls) thatextend inward from the curved outer wall 910A to a base wall 914Bproximate the opening 919.

FIG. 3 shows a top view of the resistor 920. The resistor 920 can be alow inductance resistor for a matrix converter, as further discussedbelow. The resistor 920 can be a clamp resistor used in the clamp of thematrix converter to limit an amount of current when clamping. Absentinclusion of the resistor 920, the amount of current flowing through theclamp may be high so as to cause damage to the clamp.

The resistor 920 has a generally circular shape and extends about anopening 920A generally at the center of the resistor 920. The resistor920 can include an input connector 921 with a ring connection 921A andan output connector 922 with a ring connection 922A. The resistor 920includes conductor elements 923A, 923B that extend from the input andoutput connectors 921, 922, respectively, and follow a curved serpentinepath that defines a generally circular outer perimeter 924. Theconductor elements 923A, 923B can be made of copper or other suitableelectrically conductive material.

The conductor elements 923A, 923B extend substantially parallel to eachother as they follow the curved serpentine path. As shown in FIG. 3, theconductor elements 923A, 923B define a first arcuate path 925A thatextends from the connectors 921, 922 to a curved end 925B opposite theconnectors 921, 922 and doubles back to extends along a second arcuatepath 926A (e.g., shorter than the first arcuate path 925A) that extendsto a curved end 926B proximate the connectors 921, 922. The conductorelements 923A, 923B double back from the curved end 926B and extendalong a third arcuate path 927A (e.g., shorter than the second arcuatepath 926A) to a curved end 927B opposite the connectors 921, 922. Theconductor elements 923A, 923B double back from the curved end 927B andextend along a fourth arcuate path 928A (e.g., shorter than the thirdarcuate path 927A) to a curved end 928B proximate the connectors 921,922. The conductor elements 923A, 923B double back from the curved end928B and extend along a fifth arcuate path 929A (e.g., shorter than thefourth arcuate path 928A) to a curved end 929B opposite the connectors921, 922. The conductor elements 923A, 923B double back from the curvedend 929B and extend along a curved serpentine path 930A to an end 930B.The curved serpentine path 930A can include alternating switch-backportions 931 (e.g., with three switch back turns) and straight portions932.

In one implementation, the resistor 920 can be housed in the case 910 sothat the connectors 921, 922 extend into the cutout or slot 914, and therest of the resistor 920 (e.g., the first to fifth arcuate paths 925A,926A, 927A, 928A, 929A and curved serpentine path 930A) are disposed inthe recess or cavity 912 so that the opening 920A is generally centeredover the opening 919 (e.g., so that curved serpentine wall 930A isdisposed between the curved inner wall 916 and the fifth arcuate path929A). In another implementation, the resistor 920 and case 910 are asingle piece (e.g. monolithic). For example, the resistor 920 can bedefined by at least a portion of a surface (e.g., base surface 912A) ofthe case 910. In another implementation, additionally or alternatively,the case 910 and the plate assembly P (e.g., the end-plate 400) can be asingle piece (e.g., monolithic, not detachable, without seams). Forexample, the case 910 can be defined or formed by at least a portion ofthe end wall 460 of the end-plate 400.

The resistor 920 can be made of high temperature electrical insulators(e.g., one or more sheets of thin electrical insulators (e.g., Teflon,silicon, fiberglass, rock wool). In one example, the resistor element(e.g., conductor elements 923A, 923B) can be disposed between electricalinsulator layers or sheets. In one example, the dielectric material 920can seal the case 910, allowing the resistor assembly 900 to be immersedin a bath of oil.

In certain embodiments including the one illustrated in FIG. 3, theresistor 920 can be substantially planar (e.g., flat) so that theresistor 920 (e.g., the conductor elements 923A, 923B) extends generallyalong a single plane (e.g., has a planar profile or form factor). Theconductor elements 923A, 923B can have a planar or flat form factor orprofile. The substantially planar (e.g., flat) profile or form factor ofthe resistor 920 allows the resistor 920 to be integrated in (e.g., fitwithin) the recess or cavity 912 of the case 910. Moreover, thegenerally planar profile of the resistor 920 and case 910 facilitatesincorporation of the resistor assembly 900 into the cavity 420 of theend plate 400 (see, e.g., FIG. 7), maintaining a compact overall formfactor for the motor assembly 1000. For example, the thickness of theresistor 920 and the case 910 along the central axis of the motorassembly 1000 can be substantially less than the depth of the cavity 420within the end-plate 400 along the central axis, such that the cavity420 can comfortably accommodate the resistor assembly 900. For instance,the thickness of the resistor 900 and/or the case 910 can in variousembodiments be less than about 5, 10, 15, 20, or 25 percent of the depthof the cavity 420 within the end-plate 400.

FIGS. 4A-4B show a schematic illustration of the resistor 920 inoperation. Current is applied to the input connector 921 and exits viathe output connector 922. Current flows through the conductor elements923A, 923B in a curved serpentine manner, as shown, where current flowsin one direction along the conductor element 923A and flows in anopposite direction along the conductor element 923B that is adjacent theconductor element 923A. Advantageously, the curved serpentine routing ofthe conductor elements 923A, 923B results in the magnetic fieldsgenerated in response to the current flowing through the conductorelements 923A, 923B cancelling each other out. This advantageouslyresults in the resistor 920 having a low inductance, thereby avoidingparasitic inductance that can lead to large voltages across the resistor920 during clamping.

FIG. 4B shows an enlarged partial view of the resistor 920 in FIG. 4A,showing the current flowing in one direction in the conductor element923A, and current flowing in an opposite direction in the adjacentconductor element 923B so that the magnetic fields generated by thecurrent flow in the conductor elements 923A, 923B cancel each other out,resulting in the resistor 920 having low inductance.

FIG. 5 shows a perspective view of the front side 913 of the case 910with the resistor 920 (e.g., clamp resistor) disposed in the recess orcavity 912 so that the connectors 921, 922 extend into the cutout orslot 914 and the conductor elements 923A, 923B are disposed in therecess or cavity 912 as discussed above. A dielectric material 940 isdisposed over the conductor elements 923A, 923B and at least partiallyfills (e.g., completely fills) the recess or cavity 912 of the case 910so as to define a surface 942 (e.g., so no portion of the conductorelements 923A, 923B is visible or exposed), and to define a resistorassembly 900 (e.g., a clamp resistor assembly). The surface 942 can begenerally coplanar with a plane that intersects an edge of the curvedouter wall 910A and curved inner wall 916. In one implementation, thedielectric material 940 is a ceramic material. However, other suitabledielectric materials can be used. For example, the dielectric material940 can be epoxy (a potting compound) that can suspend the resistor 920in the recess or cavity 912.

FIG. 6 shows a rear side 915 of the case 910 opposite the front side913. The rear side 915 can define a generally annular (e.g., doughnutshaped) surface 917 between the curved inner wall 916 and curved outerwall 910A of the case 910. Optionally, the surface 917 is substantiallyplanar (e.g., is flat). The faster openings 911, 918 can extend throughthe case 910 from the front side 913 to the rear side 915.

FIG. 7 shows the end-plate 400 with the resistor assembly 900 (e.g.,clamp resistor assembly) installed in a cavity or chamber 420 of theend-plate 400 defined between a circumferential outer wall 450 and anend wall 460 so that a hub 465 of the end-plate 400 extends through thecentral opening 919 of the case 910, the surface 917 is adjacent (e.g.,in contact with) the end wall 460 of the end-plate 400, and fasteners(e.g., screws, bolts) extend through the fastener openings 911, 918 ofthe case 910 to couple the case 910 to the end-plate 400 (e.g., to theend wall 460 of the end-plate 400). The input and output connectors 921,922 can be connected to other electronics in the end-plate 400 (e.g., tothe electronic module 700 (discussed further below) via electricalconnectors or cables. As shown in FIG. 7, modules 472, 474, 476, 478,480, 482 are arranged circumferentially in the chamber 420, mounted onthe end wall 460. Each of these modules 472, 474, 476, 478, 480, 482 caninclude two diodes, and can each implement one of the diode pairs1031/1034, 1032/1035, 1033/1036, 1051/1054, 1052/1055, and 1053/1056(see FIG. 13). For example, in one embodiment, the module 472 implementsdiode pair 1031/1034, the module 474 implements diode pair 1051/1054,the module 476 implements diode pair 1032/1035, the module 478implements diode pair 1052/1055, the module 480 implements diode pair1033/1036, and the module 482 implements diode pair 1053/1056. Anothermodule 484 is connected to the resistor assembly 910. The module 484includes the clamp IGBT 1043 and the clamp diode 1042. The resistorassembly 910 is connected to the terminals of the module 484 such thatthe resistor assembly 910 is connected in parallel with the clamp diode1042 and in series with the clamp IGBT 1043, as shown in FIG. 13. Theresistor assembly 910 connects to the terminals on the module 484 via aprinted circuit board that bolts down through leads on the resistorassembly 910, including the leads 921, 922, to establish the appropriateconnections.

FIG. 8 shows an exploded view of a drive module assembly 800 of theelectric motor assembly 1000. The drive module assembly 800 includes theend-plate 400 with the cavity or chamber 420 defined at least in part bythe end wall 460 and circumferential outer wall 450. The end-plate 400also has a hub 465 that defines the opening 410 at the center of theend-plate 400, and also includes the terminal box connector 440 with thechannels 430 that receive the connector wires 610 of the terminal box600. A connector cover 445 can be attached to the terminal box connector440 with one or more fasteners 447 (e.g., screws, bolts). The drivemodule assembly 800 also includes the electronics module 700, discussedfurther below, which can be housed in the chamber 420. The chamber 420has a generally circular shape and receives a similarly shapedelectronic module 700 therein. Once the electronic module 700 is in thechamber 420, the chamber 420 can be covered with one or both of anend-plate cover gasket or insulator 810 and an end-plate cover 820 usingone or more fasteners (e.g., bolts, screws) 830.

FIGS. 9-11 show features of the electronic module 700. The electronicmodule 700 can provide power and control functionality to operate theelectric motor assembly 1000 in order to drive the pump or other rotarydevice coupled to the electric motor assembly 1000. The electronicmodule 700 can have a printed circuit board or power plane assembly 710with a circular shape (e.g., annular shape with a central opening 711).The electronic module 700 can be disposed in the chamber 420 of theend-plate 400 so that the central opening 711 is disposed about the hub465 and an outer edge 701 of the printed circuit board or power planeassembly 710 is disposed inward of the circumferential outer wall 450 ofthe end-plate 400. Accordingly, the electronics can be arrangedcircumferentially about the hub 465 on the printed circuit board orpower plane assembly 710 so that the power and control electronics arehoused in the chamber 420 of the end-plate 400.

The printed circuit board or power plane assembly 710 can be amulti-layer circuit board or assembly, and can be constructed of alaminated material, such as fiberglass, which can advantageouslyinsulate the hotter power semi-conductors from more temperaturesensitive control electronics and power quality capacitors. For example,the printed circuit board or power plane assembly 710 can have a powerlayer, a control layer, a thermal barrier and a printed circuit boardlayer.

The power layer can include one or more higher temperature power modules(PM1-PM9) 718 operable to provide power to the electric motor 100. Thecontrol layer can include lower temperature control electronics modules,such as one or more power quality or input filter capacitors (IFC) 703for controlling the power provided to the electric motor 100. The powermodules (PM1-PM9) 718 can be on an opposite side of the printed circuitboard or power plane assembly 710 (e.g., on opposite sides of thethermal barrier) from the power quality or input filter capacitors (IFC)703. The thermal barrier and printed circuit board layer can be betweenthe power layer and the control layer and provide electrical connectionpaths between the power modules 718 of the power plane and the controlelectronics modules (e.g., power quality or input filter capacitors 703)of the control layer, allowing the interconnection of these components.The printed circuit board or power plane assembly 710 alsoadvantageously provides thermal insulation between the power layer andthe control layer. The printed circuit board or power plane assembly 710advantageously insulates and/or directs heat emitted from one or more ofthe power modules 718, the control electronics modules such as the inputfilter capacitors (IFC) 703 and output shaft or rotor 120 of theelectric motor 100 to the outer edge 701 of the printed circuit board orpower plane assembly 710 where higher air flow from the fan 500 isdirected.

With reference to FIG. 9, the electronic module 700 can include, inaddition to one or more (e.g., a plurality of) power quality or inputfilter capacitors (IFC) 703, a controller 702, a main power supply 704,a gate drive layer 706 and one or more clamp capacitors 708 on one sideof the printed circuit board or power plane assembly 710. With referenceto FIG. 10, the opposite side of the printed circuit board or powerplane assembly 710 can include, in addition to the power modules 718,one or more output clamp diode connections 712, a clamp insulated-gatebipolar transistor (IGBT) connection 714, one or more shunt resistorconnections 716, and one or more input filter capacitor (IFC)connections 720.

FIG. 11 shows a an assembled electronic module 700 arranged in thechamber 420 of the end-plate 400. The electronic module 700 includes oneor more input filter capacitors 703, a gate driver power supply 728, oneor more controller cards 740, one or more clamp capacitors 730, 732, 734and a clamp control circuit 738, and a copper connection 736. Theelectronic module 700 can include a matrix converter to convert amulti-phase AC input of fixed voltage and frequency into a multi-phaseAC output waveform of a desired frequency and phase. Therefore, thematrix converter is able to synthesize AC output waveforms of desiredfrequency and phase relative to the input AC waveforms. Since the rateat which electric motors, such as the electric motor 100 rotates isbased on the frequency of the applied AC input signal, using a matrixconverter to power the electric motor 100 allows for variable drivecontrol. For example, the frequency of the AC output waveform providedby the matrix converter can be changed over time to thereby operate theelectric motor 100 at the desired speed. The electronic module 700provides an embedded motor drive (EMD) that operates similar to avariable frequency drive (VFD) and that controls the input frequency andvoltage to the electric motor 100 to allow more precise speed controlfor the electric motor 100 (e.g., allowing the motor 100 to run atspeeds higher than the input line frequency). The embedded motor drive(EMD) advantageously provides for improved reliability, increasedthroughput and reduced energy consumption for the electric motorassembly 1000.

The circular shape of the electronic module 700 advantageously allows itto fit within the chamber 420 of the end-plate 400, allowing ease ofmanufacture and installation of its components. As the end-plate 400 canbe detached from the motor frame 200, maintenance of the electronicmodule 700 (e.g., to replace one or more components, such as a faulty ordamaged transistor) is simplified. Additionally, the circular shape ofthe electronic module 700 allows existing electric motor assemblies tobe retrofitted with the electronic module 700 to provide such anassembly with the embedded motor drive or variable frequency driveprovided by the electronic module 700 (e.g., by installing theelectronic module 700 in the standard sized end-plate of the electricmotor assembly).

One drawback of conventional electric motors is that they are run at afixed speed based on the input frequency of the AC power supply, andcontrol of the rotational speed of a pump or other rotary device coupledto the electric motor is provided via mechanical structure (e.g., abrake, throttle valve), resulting in a waste of energy. Another drawbackof existing electric motors is that the maximum speed of the electricmotor is limited to the AC power supply's input frequency, therebyrequiring a larger pump to be installed when increased pressure or flowof the pump is desired.

A matrix converter is a type of motor drive circuit that adjusts motorinput frequency and voltage to control AC motor speed and torque asdesired. For example, variable speed operation of an electric motor canimprove reliability and throughput while reducing energy consumption.

A matrix converter receives a multi-phase AC input voltage, and opensand closes switches of a switch array over time to thereby synthesize amulti-phase AC output voltage with desired frequency and phase. Variouscircuits are used in a matrix converter for control functions. Forinstance, a processor and/or field programmable gate array (FPGA) can beused for computations related to a modulation algorithm that selectswhich particular switches of the array are opened or closed at a givenmoment, and switch drivers can be included to provide DC control signalsto the control inputs of the switches.

The matrix converter can also include a clamp circuit that dissipatesload energy (for instance, overvoltage conditions arising duringshutdown) by clamping one or more inputs terminal of the matrixconverter to one or more output terminals of the matrix converter.Including the clamp circuit enhances robustness, for instance, byproviding a discharge path for excess load current and/or to handleovercurrent and shutdown conditions.

In certain embodiments herein, a matrix converter includes an array ofswitches having AC inputs that receives a multi-phase AC input voltageand AC outputs that provide a multi-phase AC output voltage to a load.The matrix converter further includes control circuitry that opens orcloses individual switches of the array, and a clamp circuit connectedbetween the AC inputs and AC outputs of the array and operable todissipate energy of the load in response to an overvoltage condition.The clamp circuit includes a switched mode power supply operable togenerate a DC supply voltage for the control circuitry.

Implementing the matrix converter in this manner provides a number ofadvantages, including an ability to maintain the control circuitry onfor a longer duration of time when the AC input power is lost or of poorquality.

FIG. 12 is a schematic diagram of a matrix converter 1030 according toone embodiment. The matrix converter includes an input filter 1001, anarray of switches 1002, a clamp circuit 1003, control circuitry 1004,3-phase AC input terminals 1005, and 3-phase AC output terminals 1006.

In the illustrated embodiment, the input filter 1001 is implemented asan inductor-capacitor (LC) filter that serves to filter a 3-phase ACinput voltage received on the 3-phase AC input terminals 1005 togenerate a filtered 3-phase AC input voltage for the array of switches1002. The 3-phase AC input voltage can correspond to, for example, threeAC input voltage waveforms received from a power grid and each having aphase separation of about 120° and a desired voltage amplitude (forinstance, 240 V or other desired voltage).

As shown in FIG. 12, the input filter 1001 includes a first inductor1011 connected between a first AC input terminal and a first AC input tothe array of switches 1002, a second inductor 1012 connected between asecond AC input terminal and a second AC input to the array of switches1002, and a third inductor 1013 connected between a third AC inputterminal and a third AC input to the array of switches 1002. The inputfilter 1001 further includes a first capacitor 1015 electricallyconnected between the first AC input and the second AC input of thearray of switches 1002, a second capacitor 1016 electrically connectedbetween the second AC input and the third AC input of the array ofswitches 1002, and a third capacitor 1017 electrically connected betweenthe first AC input and the third AC input of the array of switches 1002.

Including the input filter 1001 provides a number of advantages, such asproviding protection against pre-charge and/or inrush current duringpower-up. Although one implementation of an input filter is depicted,matrix converters can be implemented with input filters of a widevariety of types. Accordingly, other implementations are possible.

The control circuitry 1004 opens or closes individual switches of thearray of switches 1002 over time to thereby provide a 3-phase AC outputvoltage to the 3-phase AC output terminals 1006 with a desired frequencyand phase relative to the 3-phase AC input voltage. The controlcircuitry 1004 can include various circuits for control functions. In afirst example, the control circuitry 1004 can include a processor and/orFPGA for computations related to a modulation algorithm used to selectwhich particular switches of the array 1002 are opened or closed at agiven moment. In a second example, the control circuitry 1004 caninclude switch drivers that provide DC control signals to the switchesof the array 1002 to thereby open or close the switches as desired.

The clamp circuit 1003 is electrically connected between the AC inputsand AC outputs of the array of switches 1002, and operates to dissipateenergy during shutdown of the matrix converter 1030 or other overvoltageconditions by clamping one or more input terminals of the matrixconverter 1030 to one or more output terminals of the matrix converter1030. Including the clamp circuit 1003 enhances robustness, forinstance, by providing a discharge path for excess load current and/orto handle overcurrent and shutdown conditions. For example, the clampcircuit 1003 can prevent freewheel paths for load current duringshutdown and/or current paths for over-current.

In the illustrated embodiment, the clamp circuit 1003 includes aswitched mode power supply 1020 that serves to generate DC power for thecontrol circuitry 1004. In certain implementations, the supply voltageinput to the switched mode power supply 1020 is directly connected to atleast one internal node of the clamp circuit 1003. For example, a firstinternal node of the clamp circuit 1003 can serve to provide an inputvoltage to the switched mode power supply 1020 while a second internalnode of the clamp circuit 1003 can serve as a ground voltage to theswitched mode power supply 1020.

A switched mode power supply is an electronic power supply thatincorporates a switching regulator to convert electrical powerefficiently. For example, a switched mode power supply can convert powerusing switching devices that are turned on and off at high frequencies,and storage components such as inductors or capacitors to supply powerwhen the switching device is in a non-conductive state.

Providing the input voltage to the switched mode power supply 1020 froma node of the clamp circuit 1003 provides a number of advantages,including an ability to maintain the control circuitry 1004 on for alonger duration of time when the AC input power is lost or of poorquality.

FIG. 13 is a schematic diagram of one embodiment of a clamp circuit 1070for a matrix converter. The clamp circuit 1070 includes a switched modepower supply 1020, a first input clamping diode 1031, a second inputclamping diode 1032, a third input clamping diode 1033, a fourth inputclamping diode 1034, a fifth input clamping diode 1035, a sixth inputclamping diode 1036, a clamp capacitor 1038, a clamp resistor 1041, aclamp diode 1042, an insulated gate bipolar transistor (IGBT) 1043, adischarge activation circuit 1044, a first output clamping diode 1051, asecond output clamping diode 1052, a third output clamping diode 1053, afourth output clamping diode 1054, a fifth output clamping diode 1055,and a sixth output clamping diode 1056.

Although one embodiment of a clamp circuit for a matrix converter isdepicted, the teachings herein are applicable to clamp circuitsimplemented in a wide variety of ways. Accordingly, otherimplementations are possible.

The clamp circuit 1070 includes a first group of terminals 1061-1063that connect to the AC inputs of an array of switches, and a secondgroup of terminals 1064-1066 that connect to the AC outputs of the arrayof switches. The first group of terminals 1061-1063 includes a firstterminal 1061, a second terminal 1062, and a third terminal 1063.Additionally, the second group of terminals 1064-1066 includes a fourthterminal 1064, a fifth terminal 1065, and a sixth terminal 1066.

As shown in FIG. 13, the input clamping diodes 1031-1036 serve as aninput diode array connecting the first discharge node 1057 and thesecond discharge node 1058 to the AC inputs 1061-1063, while the outputclamping diodes 1051-1056 serve as an output diode array connecting thefirst discharge node 1057 and the second discharge node 1056 to the ACoutputs 1064-1066.

In the illustrated embodiment, the first input clamping diode 1031, thesecond input clamping diode 1032, and the third input clamping diode1033 include anodes electrically connected to the first terminal 1061,the second terminal 1062, and the third terminal 1063, respectively.Additionally, each of the first input clamping diode 1031, the secondinput clamping diode 1032, and the third input clamping diode 1033includes a cathode electrically connected to the first discharge node1057. Furthermore, the fourth input clamping diode 1034, the fifth inputclamping diode 1035, and the sixth input clamping diode 1036 includecathodes electrically connected to the first terminal 1061, the secondterminal 1062, and the third terminal 1063, respectively. Additionally,each of the fourth input clamping diode 1034, the fifth input clampingdiode 1035, and the sixth input clamping diode 1036 includes an anodeelectrically connected to the second discharge node 1058. Furthermore,the clamp capacitor 1038 is electrically connected between the firstdischarge node 1057 and the second discharge node 1058.

With continuing reference to FIG. 13, the clamp resistor 1041 iselectrically connected in series with the IGBT 1043 in a discharge pathbetween the first discharge node 1057 and the second discharge node1058. Although the IGBT 1043 illustrates one example of a dischargedevice, other implementations of discharge devices can be used.

The clamp resistor 1041 can be implemented in a wide variety of ways,including, but not limited to, using any of the embodiments of clampresistors discussed above with reference to FIGS. 1-11. For example,implementing the clamp resistor 1041 with low inductance in accordancewith the teachings herein inhibits large voltages from developing acrossthe clamp resistor 1041 during clamping.

In the illustrated embodiment, the gate of the IGBT 1043 is controlledby the discharge activation circuit 1044. In certain implementations,the discharge activation circuit 1044 selectively turns on the IGBT 1043based on monitoring a voltage difference between the first dischargenode 1057 and the second discharge node 1058. For example, the dischargeactivation circuit 1044 can activate the IGBT 1043 when the voltagedifference between the first discharge node 1057 and the seconddischarge node 1058 indicates an overvoltage condition. In certainimplementations, the discharge activation circuit 1044 provides thecontrol circuitry with an overvoltage sensing signal indicating whetheror not overvoltage has been detected.

As shown in FIG. 13, the clamp diode 1042 is connected in parallel withthe clamp resistor 1041, with an anode of the clamp diode 1042electrically connected to an intermediate node 1059 along the dischargepath. Additionally, the cathode of the clamp diode 1042 is electricallyconnected to first discharge node 1057. The clamp diode 1042 serves as afreewheeling path for any inductive voltage spike generated by the rapidswitching of the IGBT 1043 (or other semiconductor discharge device)into a parasitic inductance of the clamp resistor 1041.

In the illustrated embodiment, the switched mode power supply 1020receives an input supply voltage corresponding to a voltage differencebetween the first discharge node 1057 and the second discharge node1058, and generates a regulated DC output voltage that powers controlcircuitry of a matrix converter. For example, the second discharge node1058 can serve as a ground voltage to the switched mode power supply1020, while the first discharge node 1057 can serve as the input supplyvoltage to switched mode power supply 1020. In certain implementations,the switched mode power supply 1020 is operable over a voltage range ofat least 250 V DC to 1000 V DC, thereby enhancing performance in thepresence of fluctuations in voltage of the first discharge node 1057and/or the second discharge node 1058.

As shown in FIG. 13, the first output clamping diode 1051, the secondoutput clamping diode 1052, and the third output clamping diode 1053include anodes electrically connected to the fourth terminal 1064, thefifth terminal 1065, and the sixth terminal 1066, respectively.Additionally, each of the first output clamping diode 1051, the secondoutput clamping diode 1052, and the third output clamping diode 1053includes a cathode electrically connected to the first discharge node1057. Furthermore, the fourth output clamping diode 1054, the fifthoutput clamping diode 1055, and the sixth output clamping diode 1056include cathodes electrically connected to the fourth terminal 1064, thefifth terminal 1065, and the sixth terminal 1066, respectively.Additionally, each of the fourth output clamping diode 1054, the fifthoutput clamping diode 1055, and the sixth output clamping diode 1056includes an anode electrically connected to the second discharge node1058.

FIG. 14 is a schematic diagram of one embodiment of a portion ofcircuitry 1100 of a matrix converter. The circuitry 1100 includes anarray of switches 1102, switch drivers 1106 a-1106 i that drivebidirectional switches 1107 a-1107 i of the array 1102, a controlcircuit 1104 that generates input control signals to the switch drivers1106 a-1106 i, isolated DC-to-DC converters 1105 a-1105 i that power theswitch drivers 1106 a-1106 i, and a switched mode power supply 1020 thatpowers the control circuit 1104 and the isolated DC-to-DC converters1105 a-1105 i.

As shown in FIG. 14, the array of switches 1102 includes a firstbidirectional switch 1107 a connected between a first AC input 1121 anda first AC output 1124, a second bidirectional switch 1107 b connectedbetween the first AC input 1121 and a second AC output 1125, a thirdbidirectional switch 1107 c connected between the first AC input 1121and a third AC output 1126, a fourth bidirectional switch 1107 dconnected between the second AC input 1122 and the first AC output 1124,a fifth bidirectional switch 1107 e connected between the second ACinput 1122 and the second AC output 1125, a sixth bidirectional switch1107 f connected between the second AC input 1122 and the third ACoutput 1126, a seventh bidirectional switch 1107 g connected between thethird AC input 1123 and the first AC output 1124, an eighthbidirectional switch 1107 h connected between the third AC input 1123and the second AC output 1125, and a ninth bidirectional switch 1107 iconnected between the third AC input 1123 and the third AC output 1126.

The bidirectional switches 1107 a-1107 i serve to conduct both positiveand negative currents, and are implemented to be able to block bothpositive and negative voltages.

As shown in FIG. 14, each of the bidirectional switches 1107 a-1107 ireceive a pair of switch control signals. In particular, thebidirectional switches 1107 a-1107 i receive first to ninth pairs ofswitch control signals from switch drivers 1106 a-1106 i, respectively.The switch drivers 1106 a-1106 i receive first to ninth pairs of inputsignals from the control circuit 1104. By controlling the state of theinput signals over time, the control circuit 1104 achieves a desiredmodulation algorithm, such as Venturini modulation, Alesina modulation,scalar modulation, fictitious DC-link modulation, and/or space vectormodulator. Furthermore, the control circuit 1104 generates the inputsignals to provide current commutation and/or other desired switchingproperties.

In the illustrated embodiment, the switched mode power supply 1020receives an input voltage from internal node(s) of a clamp circuit (notshown in FIG. 14) and generates a DC voltage that powers the controlcircuit 1104. Additionally, the DC voltage serves as an input to theisolated DC-to-DC converters 1105 a-1105 i, respectively. The isolatedDC-to-DC converters 1105 a-1105 i in turn provide first to ninth DCvoltages to the switch drivers 1106 a-1106 i, respectively. The isolatedDC-to-DC converters 1105 a-1105 i can be implemented in a wide varietyof ways, including, but not limited to, as flyback converters.

FIGS. 15A-15C illustrate various embodiments of bidirectional switchesfor an array of switches of a matrix converter. Although variousexamples of bidirectional switches are shown, the teachings herein areapplicable to bidirectional switches implemented in a wide variety ofways.

FIG. 15A is a schematic diagram of a bidirectional switch 1600 accordingto one embodiment. The bidirectional switch 1600 includes a first IGBT1601, a second IGBT 1602, a first diode 1603, and a second diode 1604.The bidirectional switch 1600 is arranged in a common emitterback-to-back IGBT configuration.

As shown in FIG. 15A, the gate of the first IGBT 1601 receives a firstcontrol signal CTL1, and the gate of the second IGBT 1602 receives asecond control signal CTL2. Additionally, the collector of the firstIGBT 1601 is electrically connected to an input terminal IN and to acathode of the first diode 1603, and the emitter of the first IGBT 1601is electrically connected to the emitter of the second IGBT 1602 and tothe anodes of the first diode 1603 and the second diode 1604.Furthermore, the collector of the second IGBT 1602 is electricallyconnected to an output terminal OUT and to a cathode of the second diode1604.

FIG. 15B is a schematic diagram of a bidirectional switch 1620 accordingto another embodiment. The bidirectional switch 1620 includes a firstIGBT 1621, a second IGBT 1622, a first diode 1623, and a second diode1624. The bidirectional switch 1620 is arranged in a common collectorback-to-back IGBT configuration.

As shown in FIG. 15B, the gate of the first IGBT 1621 receives a firstcontrol signal CTL1, and the gate of the second IGBT 1622 receives asecond control signal CTL2. Additionally, the emitter of the first IGBT1621 is electrically connected to an input terminal IN and to an anodeof the first diode 1623, and the collector of the first IGBT 1621 iselectrically connected to the collector of the second IGBT 1622 and tothe cathodes of the first diode 1623 and the second diode 1624.Furthermore, the emitter of the second IGBT 1622 is electricallyconnected to an output terminal OUT and to an anode of the second diode1624.

FIG. 15C is a schematic diagram of a bidirectional switch 1640 accordingto another embodiment. The bidirectional switch 1640 includes a firstbidirectional IGBT 1641 and a second bidirectional IGBT 1642. Thebidirectional switch 1640 is arranged in a reverse blocking IGBTconfiguration.

As shown in FIG. 15C, the gate of the first bidirectional IGBT 1641receives a first control signal CTL1, and the gate of the secondbidirectional IGBT 1642 receives a second control signal CTL2.Additionally, a collector/emitter of the first bidirectional IGBT 1641is electrically connected to the input terminal IN and to theemitter/collector of the second bidirectional IGBT 1642, and anemitter/collector of the first bidirectional IGBT 1641 is electricallyconnected to the output terminal OUT and to the collector/emitter of thesecond bidirectional IGBT 1642. Thus, the first bidirectional IGBT 1641and the second bidirectional IGBT 1642 serves as a pair of switchingdevices arranged in anti-parallel.

With respect to FIGS. 15A-15C, the first control signal CTL1 and thesecond control signal CTL2 are provided by a switch driver.Additionally, the input terminal IN couples to an AC input of a switcharray, while the output terminal OUT couples to an AC output of a switcharray.

FIG. 16 is a schematic diagram of a matrix converter 1700 according toanother embodiment. The matrix converter 1700 is providing power to amotor 1718, and includes an input filter 1701, an array of switches1702, a clamp circuit 1703, a control circuit 1704, 3-phase AC inputterminals 1705, 3-phase AC output terminals 1706, input voltagetransducers 1711, isolated DC-to-DC converters 1712, switch drivers1713, a heat sink 1714, output current transducers 1715, currentdirection sensors 1716, and a shaft position sensor 1717.

As shown in FIG. 16, the clamp circuit 1703 includes a switched modepower supply 1720 that generates a regulated DC voltage that powers thecontrol circuit 1704 and that serves as an input voltage to the isolatedDC-to-DC converters 1712. The isolated DC-to-DC converters 1712 (forinstance, flyback converters) output DC voltages that power the switchdrivers 1713.

With continuing reference to FIG. 16, the control circuit 1714 iselectrically connected to an interface, such as a serial interface orbus. The interface can connect to a network to facilitate remote controlover the matrix converter 1700 and motor 1718. Additionally, the controlcircuit 1714 includes digital processing circuitry 1731 (for instance, aprocessor and/or FPGA) that digitally processes data, and dataconverters 1732 that provide analog-to-digital conversion anddigital-to-analog conversion operations. For example, the dataconverters 1732 can serve to provide conversion of signals received fromthe depicted sensors and transducers.

The control circuit 1714 receives a variety of signals that indicateoperating conditions of the matrix converter 1700. For example, in theillustrated embodiment, the control circuit 1714 receives input voltagesensing signals from the input voltage transducers 1711, an overvoltagesensing signal from the clamp circuit 1703 (for example, from adischarge activation circuit of the clamp circuit 1703), a temperaturesensing signal from the heat sink 1714, output current sensing signalsfrom the output current transducers 1715, current direction sensingsignals from the current direction sensors 1716, and a shaft positionsensing signal from the shaft position sensor 1717.

Implementing the matrix converter 1700 with such sensors provides anumber of functions, such as over-current trip protection, over-voltagetrip protection, thermal trip protection, and/or enhanced control overrotation, torque, and/or speed of the motor 1718.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the systems and methodsdescribed herein may be made without departing from the spirit of thedisclosure. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the disclosure. Accordingly, the scope is defined only byreference to the appended claims.

Features, materials, characteristics, or groups described in conjunctionwith a particular aspect, embodiment, or example are to be understood tobe applicable to any other aspect, embodiment or example described inthis section or elsewhere in this specification unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The protection is notrestricted to the details of any foregoing embodiments. The protectionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

Furthermore, certain features that are described in this disclosure inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations, one or more features from a claimedcombination can, in some cases, be excised from the combination, and thecombination may be claimed as a subcombination or variation of a subcombination.

Moreover, while operations may be depicted in the drawings or describedin the specification in a particular order, such operations need not beperformed in the particular order shown or in sequential order, or thatall operations be performed, to achieve desirable results. Otheroperations that are not depicted or described can be incorporated in theexample methods and processes. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the described operations. Further, the operations may berearranged or reordered in other implementations. Those skilled in theart will appreciate that in some embodiments, the actual steps taken inthe processes illustrated and/or disclosed may differ from those shownin the figures. Depending on the embodiment, certain of the stepsdescribed above may be removed, others may be added. Furthermore, thefeatures and attributes of the specific embodiments disclosed above maybe combined in different ways to form additional embodiments, all ofwhich fall within the scope of the present disclosure. Also, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the describedcomponents and systems can generally be integrated together in a singleproduct or packaged into multiple products.

For purposes of this disclosure, certain aspects, advantages, and novelfeatures are described herein. Not necessarily all such advantages maybe achieved in accordance with any particular embodiment. Thus, forexample, those skilled in the art will recognize that the disclosure maybe embodied or carried out in a manner that achieves one advantage or agroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements, and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements, and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements, and/or steps areincluded or are to be performed in any particular embodiment.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,”“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than 10% of, within less than 5% of, within less than 1% of, withinless than 0.1% of, and within less than 0.01% of the stated amount. Asanother example, in certain embodiments, the terms “generally parallel”and “substantially parallel” refer to a value, amount, or characteristicthat departs from exactly parallel by less than or equal to 15 degrees,10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

The scope of the present disclosure is not intended to be limited by thespecific disclosures of preferred embodiments in this section orelsewhere in this specification, and may be defined by claims aspresented in this section or elsewhere in this specification or aspresented in the future. The language of the claims is to be interpretedbroadly based on the language employed in the claims and not limited tothe examples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive.

What is claimed is:
 1. An electric motor assembly for driving a rotarymachine, the motor assembly comprising: an electric motor having anoutput shaft that extends along a central axis of the electric motor,the electric motor being operable to rotate the output shaft; a motorframe that houses the electric motor so that the output shaft protrudesfrom an end of the motor frame; a first plate having a cavity configuredto house motor drive electronics; and a resistor assembly within thecavity, the resistor assembly comprising: a case defining a recess; anda resistor within the case, the resistor comprising an input, an output,and a conductor extending from the input to the output and forming aplurality of nested arcuate paths arranged such that current flows inopposite directions through adjacent segments of the plurality of nestedarcuate paths, wherein magnetic fields generated by the current flowcancel each other.
 2. The assembly of claim 1, wherein an outer wall ofthe case has a generally circular shape.
 3. The assembly of claim 2,wherein the case is removably coupleable to the first plate and furthercomprises a cutout defined by a pair of walls extending from the outerwall to an end wall proximate a curved inner wall of the case, the inputand output configured to extend into the cutout when the resistor ishoused in the case.
 4. The assembly of claim 1, wherein the resistorforms a generally planar shape.
 5. The assembly of claim 4, wherein theconductor of the resistor forms a curved serpentine path.
 6. Theassembly of claim 1, further comprising a dielectric material disposedover the resistor so that at least a portion of the resistor is disposedbetween the dielectric material and a base wall of the case, thedielectric material defining a generally planar front surface of theresistor assembly.
 7. The assembly of claim 1, further comprising asecond plate having an opening configured to receive the output shafttherethrough, the second plate being coupleable about the output shaftproximate to the end of the motor frame between the first plate and theend of the motor frame.
 8. A plate assembly configured for use with anelectric motor assembly, the plate assembly comprising: a first platehaving a cavity that houses motor drive electronics; and a resistorwithin the cavity, the resistor comprising an input, an output, and aconductor extending from the input to the output and forming a pluralityof nested arcuate paths arranged such that current flows in oppositedirections through adjacent segments of the plurality of nested arcuatepaths and magnetic fields generated by the current flow cancel eachother.
 9. The plate assembly of claim 8, further comprising a casedetachable from the plate assembly, the case defining a recessconfigured to receive at least a portion of the resistor therein. 10.The plate assembly of claim 8, wherein the resistor is generally planar.11. The plate assembly of claim 8, wherein the conductor forms a curvedserpentine path.
 12. The plate assembly of claim 8, further comprising adielectric material disposed over the resistor.
 13. The plate assemblyof claim 8 further comprising a second plate having an openingconfigured to receive a motor output shaft therethrough, the secondplate being coupleable about the output shaft proximate to an end of amotor frame between the first plate and the end of the motor frame. 14.A resistor for a motor drive circuit of an electric motor assembly, theresistor comprising: an input; an output; and a conductor extending fromthe input to the output and forming a plurality of nested arcuate pathsarranged such that current flows in opposite directions through adjacentsegments of the plurality of nested arcuate paths and magnetic fieldsgenerated by the current flow cancel each other.
 15. The resistor ofclaim 14, wherein the conductor is formed in a curved serpentine path.16. The resistor of claim 14, wherein the conductor forms a generallyplanar shape.
 17. The resistor of claim 14, further comprising a casehaving a generally annular shape with a curved outer wall, a curvedinner wall that defines a central opening of the case, and a base wall,a recess defined by and between the curved inner wall, the curved outerwall and the base wall, wherein the conductor is configured to bedisposed in the recess between the curved inner wall and curved outerwall of the case.
 18. The resistor of claim 17, wherein the case furthercomprises a cutout defined by a pair of walls extending from the curvedouter wall to an end wall proximate the curved inner wall, the input andoutput configured to extend into the cutout when the conductor is housedin the recess.
 19. The resistor of claim 17, further comprising adielectric material disposed over the conductor so that at least aportion of the conductor is disposed between the dielectric material andthe base wall of the case.
 20. The resistor of claim 19, wherein thedielectric material is a ceramic material.